CMYK (cyan, magenta, yellow, black) profiling of prepress proofing systems and output devices such as inkjet is fairly commonly practiced in many International Color Consortium (ICC) profiling solutions. Far more challenging is the profiling of N-color systems, printing presses, and particularly flexo printing presses due to inconsistency and variability of color measurements across the sheet, sheet-to-sheet, and run-to-run. N-color profiling of such systems is made even more complicated by the ever increasing size of color data sets required in order to build a profile with increasing N.
Both press variability and N-color profiling require many hours of manual labor to perform measurements, sort out bad data, and obtain average sets of measurements that are reliable for purposes of profiling. There is also a high cost to printing large charts due to the cost of plates, ink, paper, and manual labor. It is highly desirable therefore to develop better methods of profiling that have the potential of greatly reducing the amount of measurements required.
Physical modeling of output systems using Neugebauer, Kubelka-Munk, etc. has been shown useful in various applications (U.S. Pat. No. 6,232,954 (Rozzi); U.S. Pat. No. 7,710,597 (Edge); and U.S. Pat. No. 7,738,142 (Edge)). Since such models can define a system based on its fundamental properties such as ink density, spectral reflectance, dot gain, ink opacity, etc. there is the possibility of reducing the amount of data required in order to build a profile as well as the possibility of updating an existing profile based on changes in density, dot gain, etc.
Prior art models that attempt to solve this problem include Cellular Neugebauer (CN) and “NeugX.” The former is a mature technology that currently provides optimal results given a reasonably well-sampled data set. NeugX is based on a hybrid physical model combining Neugebauer and Kubelka-Munk. As such, the latter model can be updated based on minimal information, such as changes in the density or hue of the primary inks, and tone properties. Both models require processing large amounts of data. The “revised NeugX” model described herein adds the ability to adjust the spectral Yule-Nielson n-factor as a function of device coordinates in order to characterize imaging systems whose behavior deviates significantly from a simple Neugebauer model.
Building profiles based on smaller amounts of chart data is of great value due to the high cost of printing sheets dedicated to images of measurement charts.